Russia has blocked action in the Security Council to criticize the regime of Syrian President Bashar al-Assad.

Britain had circulated a draft statement expressing outrage over Syrian government air strikes in the northern city of Aleppo, where it said more than 700 people have been killed and 3,000 injured since December 15.

Diplomats are quoted by news agencies as saying Russia added amendments to the statement which were, in the words of one official quoted by Reuters, "clearly designed to rob the statement of any reference to what happened in Aleppo."

Russia, a staunch Assad ally, opposed a similar statement on December 19 that would have condemned attacks by Syrian government troops on civilians.

Russia, joined by China, has also vetoed three Security Council resolutions that would have condemned Assad's government.